nest – SDP Offer WebRTC

I’m trying to execute the sdm.devices.commands.CameraLiveStream.GenerateWebRtcStream command on a Nest Battery Cam which only support WebRTC streams. The request should be as follows:

POST /enterprises/$project-id/devices/$device-id:executeCommand
{
  "command" : "sdm.devices.commands.CameraLiveStream.GenerateWebRtcStream",
  "params" : {
    "offerSdp" : "$offerSdp"
  }
}

According to another answered question the following code generates a correct SDP offer which is accepted by Google:

const myPeerConnection = new RTCPeerConnection

myPeerConnection.createDataChannel("dataSendChannel");

myPeerConnection.createOffer({offerToReceiveAudio:!0,offerToReceiveVideo:!0}).then(function(offer) {
    return myPeerConnection.setLocalDescription(offer);
  })
  .then(function() {
    console.log(myPeerConnection.localDescription.sdp + "n");
  })
  .catch(function(reason) {
    console.log("An error occurred, so handle the failure to connect");
  });

Has anyone an idea how to “generate” from the last code the $offerSdp to be inserted in the first code?